Method and apparatus for producing composite fillers

ABSTRACT

Apparatus for producing a composite filler includes at least one die and a device for moving a stack of reinforced ply strips through the die. The die has peripheral die face adapted for forming the ply strip stack into a desired cross sectional shape. The cross section of the die face may vary around the periphery of the die.

BACKGROUND INFORMATION

1. Field

The present disclosure generally relates to the fabrication compositestructures, and deals more particularly with a method and apparatus forproducing fillers used to fill gaps in such structures.

2. Background

Composite structures may be fabricated by joining two or more memberstogether. In some cases, there may be one or more gaps in areas ofjoints between the members that may reduce the strength of the joints.In order to strengthen the joints, the gaps are filled with fillers,sometimes also referred to as radius fillers, fillets or noodles. Thefiller may be formed from composite materials such as adhesive, prepregtape or fabric. In some cases, the cross section of the gap may vary insize and/or shape along its length as a result of the adjoiningcomposite members converging or diverging from each other. For example,ply pad-ups, ply drop-offs and/or joggles on a composite skin may resultin a variable gap between the skin and an overlying stiffener, such as astringer, that is attached to the skin.

In the past, fillers having variable cross sectional shapes werefabricated using hand layup techniques that involved laminatingunidirectional fiber prepreg tape, in which the fiber orientation wasparallel to the length of the gap. This hand layup technique requiredmultiple processing steps, was labor intensive and time consuming.Additionally, fillers employing unidirectional fiber reinforcement maybe subject to movement and may not exhibit the desired degree ofresistance to cracking.

Accordingly, there is a need for a method and apparatus for producing acomposite filler having a variable cross section along its length, thatare reliable and repeatable, and which reduce labor costs by automatingthe fabrication process. There is also a need for a method and apparatusas described above which result in a filler having improved stiffness,toughness and/or resistance to cracking.

SUMMARY

The disclosed embodiments provide a method and apparatus for producing acomposite filler having improved toughness and strength, and whichreduces the time and labor required to produce a filler having varyingcross section along its length. Improved filler toughness and strengthand achieved by laminating plies of fiber prepreg in which the laminatedplies have varying fiber orientations. The method may be carried out byautomated equipment that produces laminated fillers of a desired lengthand varying cross sectional shape and/or area. The apparatus allows anadhesive to be automatically applied to the outer surfaces of thefiller, without the need for hand labor. Composite fillers may beproduced more quickly and with more repeatable results, using fewerprocessing steps.

According to one disclosed embodiment, apparatus is provided forproducing a composite filler comprising a rotatable die and a device formoving a stack of reinforced strips through the die. The die has aperipheral die face adapted for forming a stack of strips into a desiredcross sectional shape. The cross section of the die varies around itsperiphery. The device for pulling the stack of strips through the diecomprises a puller. The apparatus may further comprise a plurality ofcreels each adapted to hold and dispense one of the strips, and a guidefor directing the strips dispensed from the creels into a stack. Theguide may include a plurality of aligned slots for respectively guidingthe strips into the stack. The apparatus may further comprise a cut andadd device for cutting the strips dispensed from the creels andselectively adding strips dispensed to the guide. The apparatus may alsocomprise a heated chute for guiding and heating the stack of strips thatare formed by the die. The die may be substantially circular in shapeand rotates about a central axis. The die face may include at least afirst circumferential section having a substantially constant crosssectional area, and a second circumferential section having a varyingcross sectional area. The apparatus may further comprise a slitter forslitting a layup of prepreg plies into a plurality of prepreg strips,and a redirect device for redirecting the cut prepreg strips intostacked relationship.

According to another disclosed embodiment, apparatus is provided forproducing a composite filler, comprising a slitter adapted to slit amulti-ply composite layup into a plurality of side-by-side strips, and aredirect device for redirecting the side-by-side strips into a stack.The apparatus further comprises a forming die for forming the stack ofcomposite strips into a desired cross sectional shape, and a puller forpulling the stack substantially continuously through the slitter, theredirect device and the forming die. The redirect device may includerollers for changing the orientation of the composite prepreg stripsrelative to each other. The forming die is rotatable and includes asubstantially circular die face having a variable cross section aroundits periphery.

According to still another embodiment, a method is provided offabricating a composite filler having a cross section that varies alongits length. The method comprises forming a stack of composite prepregstrips, feeding the stack of strips through at least one die, and usingthe die to form the stack of strips, including varying the shape of theface of the die in contact with the stack as the stack is fed throughthe die. Varying the shape of the die face includes rotating the die asthe stack is fed through the die. Forming the stack of strips includesdispensing strips of composite prepreg respectively from a plurality ofcreels and aligning the strips with each other into a stack.

According to another embodiment, a method is provided of fabricating acomposite filler. The method comprises forming a multi-ply compositelayup, feeding the layup substantially continuously through a slitterand at least one forming die, and using the slitter to slit the layupinto a plurality of side-by-side composite prepreg strips. The methodfurther comprises aligning the composite prepreg strips into a stack asthe composite prepreg strips are fed from the slitter to the formingdie, and using the die to form the stack of composite strips into thefiller. Forming the layup may include laying up unidirectional fiberprepreg plies having at least two different fiber orientations.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the advantageousembodiments are set forth in the appended claims. The advantageousembodiments, however, as well as a preferred mode of use, furtherobjectives and advantages thereof, will best be understood by referenceto the following detailed description of an advantageous embodiment ofthe present disclosure when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an illustration of a perspective view of a composite filler.

FIG. 2 is an illustration of a cross sectional, perspective view showinggaps between a stringer and a skin that may be filled with a compositefiller.

FIG. 3 is an illustration of an end view of the filler shown in FIG. 1.

FIG. 4 is an illustration of an end view of a filler having an alternatecross sectional shape.

FIG. 4A is an illustration of a cross sectional view of a portion ofthree structural members of an I-beam being joined together and having agap therebetween filled by the filler shown in FIG. 4.

FIG. 5 is an illustration of a perspective view of a filler having across sectional area that varies along its length.

FIG. 6 is an illustration of an end view taken in a direction designatedas FIG. 6 in FIG. 5.

FIG. 7 is an illustration of a functional block diagram of apparatus forproducing the filler shown in FIGS. 5 and 6.

FIG. 8 is an illustration of an exploded, perspective view of a plylayup that may be used to fabricate a filler using the apparatus shownin FIG. 7.

FIG. 9 is an illustration of an end view of the ply layup shown in FIG.8.

FIG. 10 is an illustration of an end view showing the ply layup of FIG.9 having been slit into individual prepreg strips.

FIG. 11 is an illustration of a diagrammatic, side view of oneembodiment of the apparatus shown in FIG. 7.

FIG. 12 is an illustration of a diagrammatic side view showingadditional details of the apparatus shown in FIG. 11.

FIG. 13 is an illustration of a ply strip guide taken in the directionshown as FIG. 13 in FIG. 12.

FIG. 14 is an illustration of an end view of a stack of the ply strips,prior to being formed by the die.

FIG. 15 is an illustration of an end view of the forming die taken inthe direction shown as FIG. 15 in FIG. 12.

FIG. 15A is an illustration of a side view taken in the direction shownas 15A in FIG. 15.

FIG. 16 is a rectilinear layout of the circumference of the die shown inFIGS. 12 and 15, taken along the line 16-16.

FIG. 17 is an illustration similar to FIG. 12, but showing an alternateembodiment of the apparatus employing an adhesive applicator.

FIG. 18 is an illustration of a flow diagram of a method of fabricatinga composite filler having a cross section that varies along its length.

FIG. 18A is an illustration of a flow diagram of an alternate method offabricating a composite filler.

FIG. 19 is an illustration of a flow diagram illustrating additionalsteps of the method shown in FIG. 18.

FIG. 20 is an illustration of a diagrammatic side view of an alternateform of the apparatus employing a ply slitter.

FIG. 21 is an illustration of a plan view of the apparatus shown in FIG.20.

FIG. 22 is an illustration of a sectional view taken along the line22-22 in FIG. 21.

FIG. 23 is an illustration of a flow diagram of a method of fabricatinga composite filler using the apparatus shown in FIGS. 20 and 21.

FIG. 24 is an illustration of a flow diagram showing additional steps ofthe method shown in FIG. 23.

FIG. 25 is an illustration showing the sequential steps performed by theapparatus shown in FIGS. 20 and 21.

FIG. 26 is a side view of an alternate embodiment of the apparatusemploying a pair of forming dies.

FIG. 27 is an illustration of a perspective view of a filler produced bythe apparatus shown in FIG. 26.

FIG. 28 is an illustration of an end view of the forming dies shown inFIG. 26.

FIG. 29 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 30 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIGS. 1-3, the disclosed embodiments relate to amethod and apparatus for producing a composite filler 30 suitable forfilling gaps 34 between composite members, such as, without limitation,a stringer 36 attached to a skin 38. The stringer 36 includes a hatsection 40 joined to a pair of flanges 42 by a radius section 43 thatresults in gaps 34 that are generally triangular in cross sectionalshape along the length of the stringer 36. In some applications, thecross section of the gaps 34 may vary along the length of the gap 34,either in its area or in its shape, or both. This variance may becaused, for example and without limitation, by ply drop-offs, pad-ups,or joggles (not shown) in the skin 38, and/or curvatures in either thestringer 36 or the skin 38. The stringer 36 and skin 38 are merelyillustrative of a wide range of joined structural members havingvariable gaps 34 that may require a filler 30 in order to improvestructural performance.

Referring to FIG. 3, the filler 30 may comprise a plurality of laminatedplies 44 of unidirectional fiber prepreg. As will be discussed laterbelow in more detail, the fiber orientations of the plies 44 may be thesame or different, according to a predetermined ply schedule suitablefor the application. In the illustrated example, the filler 30 has agenerally triangular cross sectional shape 32 formed by three sides 46.Other cross sectional shapes 32 are possible. For example, FIG. 4illustrates a filler 30 having a substantially flat side 46 and tworadiused sides 46 a. The filler 30 shown in FIG. 4 may be suitable foruse in filling a gap 34 between a pair of back-to-back L or U-shapedshaped structural members 35, and a cap 37 that are joined together toform an I-Beam (only partially shown in FIG. 4A). The cross sectionalshapes of the fillers 30 shown in FIGS. 1 and 4 are merely illustrativeof a wide range of cross sectional shapes that are possible. Forexample, and without limitation, the cross sectional shape of filler 30may have any number of straight sides, curves or a combination of curvesand straight sides which may vary in area or geometry along the lengthof the filler 30, and which may correspond to the changing crosssectional profile of the gap 34 along its length. A filler 30 having across sectional shape formed by straight sides at one end of the filler30 may transition either linearly or non-linearly, into a crosssectional shape having one or more curves at any point along the lengthof the filler 30.

Referring now to FIGS. 5 and 6, as previously discussed, in someapplications the cross section of the filler 30 may vary along itslength. For example, the cross sectional shape 32 and/or the crosssectional area 58 of the filler 30 may vary continuously or along onlyportions of the length of the filler 30. In the example shown in FIGS. 5and 6, the cross sectional shape 32 remains the same, i.e. remainstriangular, throughout the length of the filler, however the height Hand width W₁, and thus the area of the cross section varies. Forexample, the cross sectional area 58 at one end 48 increases steadily at54 to an intermediate section 52 where the cross sectional area 58remains substantially constant, but then steadily decreases at 56 to theother end 50. The cross sectional area 58 of the filler 30 is greatestand remains substantially constant throughout the intermediate section52, but varies linearly throughout sections 54 and 56. As previouslystated, the cross sectional area 58 may vary at any rate of increase ordecrease, or remain constant at any section along the length of thefiller 30.

Referring now to FIG. 7, apparatus generally indicated at 55 forproducing a composite filler 30 broadly comprises a source 60 ofpre-plied fiber reinforced strips 84, hereinafter referred to ply stripsor reinforced strips 84 are pulled through a delivery head 62 by apuller 64. The delivery head 62 includes a ply strip guide 66 thatdirects the ply strips 84 through cut/add heads 68 into an ordered plystack 92. At least one forming die 70 is employed to form the ply stripstack 92 into a filler 30 having the desired cross sectional shapeand/or size along its length. In some embodiments, the ply strip stack92 may be directed by the guide 66 through more than one forming die 70.The cut/add heads 68 are operated by control signals issued by thecontroller 72 (FIG. 7) and may comprise devices similar to thosedescribed in U.S. Pat. No. 4,699,683, issued Oct. 13, 1987, U.S. Pat.No. 7,213,629 issued May 8, 2007 and US Patent Publication No.20070029030A1 published Feb. 8, 2007, the entire contents of which areincorporated by reference herein. In one embodiment, the ply stripsource 60 may comprise a composite ply layup 74 (FIG. 9) that is slitinto individual ply strips 84 (FIG. 10) either before or after enteringthe delivery head 62. The prep-plied layup 74 may be slit into the plystrips 84 using any suitable cutting device, such as for example andwithout limitation, a Gerber cutter. The ply strip source 60 along withthe cut/add heads 68, forming die 70 and puller 64 may be operated by acontroller 72 which may comprise a PC or a PLC (programmable logiccontroller) that outputs control signals on lines 73.

Referring now to FIGS. 8, 9 and 10, as previously mentioned, the filler30 may be formed from a ply layup 74 comprising a plurality of plies 76of unidirectional fiber prepreg that are assembled ply-by-ply, accordingto a predetermined supply schedule (not shown), using either hand-layuptechniques or an AFP (automatic fiber placement) machine (not shown).The fiber orientation of the plies 76 may vary from ply-to-ply. Forexample, as shown in FIG. 8, the plies 76 may have a 0 degree fiberorientation 78, a 45 degree fiber orientation 80, or a 90 degree fiberorientation 82, as well as other orientations within a particular layup74. The ply layup may include plies having at least two types for fiberreinforcing fibers, such as glass fibers and carbon fibers, in order tofabricate fillers 30 known as “hybrid fillers”. Other fiberreinforcements are possible. Following assembly, the ply layup 74 (FIG.9) is slit into a plurality of ply strips 84 as shown in FIG. 10, eachcomprising one or more individual plies 76 of the same or differingfiber orientations. The ply strips 84 may vary in width W₂, dependingupon the cross sectional shape of the filler 30 being fabricated.

Attention is now directed to FIG. 11 which broadly illustratescomponents of one embodiment of the apparatus 55. In this example, theply strip source 60 comprises a plurality of creels 86 respectivelywound with ply strips 84 that may be of differing widths W₂ (FIG. 10). Aset of take-up reels 88 are provided to take up backing paper 85 that isremoved from the ply strips 84 as they are dispensed from the creels 86.The ply strips 84 dispensed from the creels 86 are aligned with eachother and fed as a group 90 to a delivery head 62 where the ply strips84 are guided into a stack 92 (FIG. 14) that is heated to a formingtemperature and formed by at least one die 70 into the final crosssectional shape of the filler 30. As previously mentioned, in someembodiments, the stack 92 may formed into the final cross sectionalshape using more than one of the dies 70. The stack 92 is moved throughthe delivery head 62 by a suitable motorized puller 64 which pulls theformed filler 30 in the direction shown by the arrow 65 over a flatlower die 94, causing the ply strips 84 to be drawn from the creels 86.Operation of the puller 64 is controlled by the controller 72 shown inFIG. 7. The process of pulling the stack 92 through the delivery headand drawing ply strips 84 from the creels 86 is carried outsubstantially continuously and automatically until the desired length ofthe filler 30 is completed. In some embodiments, the operation of thecreels 86 may be controlled by control signals from the controller 72shown in FIG. 7.

FIG. 12 illustrates additional details of the apparatus 55 shown in FIG.11. The ply strips 84 dispensed from creels 86 respectively pass throughcut/add heads 68 which cut and add ply strips 84 as required, to thelengths needed to produce a filler 30 of a desired length. The plystrips 84 pass, as a group 90, through a guide 66 shown in FIGS. 12 and13 which includes a plurality of aligned slots 100. The slots 100 alignthe ply strips 84 and guide them into a chute 96 that may be heated byany suitable means at 98. The chute 96 funnels the aligned ply strips 84into an ordered stack 92 shown in FIG. 14 which has a cross section thatroughly approximates the cross sectional shape and area of the completedfiller 30. The chute 96 also heats the stack 92 to a forming temperatureand guides the stack 92 into a nip 97 between the forming die 70 andflat lower die 94, drawn by the force applied to the stack 92 by thepuller 64 (FIG. 11) as the puller 64 pulls the completed filler 30 inthe direction shown by the arrow 65. The lower die 94 may or may notform an extension of the heated chute 96. The die 70 may be driven torotate by a motor (not shown) operated by the controller 72 shown inFIG. 7 which synchronizes the rotation of the die 70 with the speed ofthe puller 64. As previously noted, more than one die 70 may be employedin series to form the stack 92 into the desired cross sectional shape.

Referring now to FIGS. 12, 15, 15A and 16, the forming die 70 isgenerally circular about a central axis of rotation 95. The die 70includes a concave die cavity 104 (FIG. 15) formed by a peripheral dieface 102. In the illustrated example, the die cavity 104 is generallytriangular in cross sectional shape, and has a depth D₁ and a width W₃that vary around the circumference of the die 70. Thus, the crosssection of the die face 102 in contact with the stack 92 of ply strips84 may vary as the die 70 rotates and the stack 92 moves through the die70. FIG. 16 schematically illustrates the varying cross section profileof the die cavity 104, represented by the change in depth D₁ around thecircumference of the die 70. The depth D₁ increases steadily from adepth D₁ at 106 to a depth D₂ at 108 and then decreases to D₁ at 110. Asis apparent from FIG. 16, the cross sectional profile of the die cavity104 substantially corresponds to the cross sectional shape of the filler30 shown in FIGS. 5 and 6. The die cavity 104 may have any of a varietyof other cross sectional shapes that vary around the circumference ofthe die 70, depending on the geometry of the filler 30 being fabricated.As previously mentioned, the controller 72 (FIG. 7) controls therotational position of the die 70 and synchronizes the die's rotationalposition with the rate at which the puller (FIGS. 7 and 10) pulls thefiller 30 through the die 70 in order to vary the die face 102 incontact with the ply stack 92 as the ply stack passes into the nip 97.

In some applications, it may be desirable to apply an adhesive to outersurfaces of the filler 30 which aids in bonding the filler 30 tosurrounding structural members forming the gap 34 shown in FIG. 2, suchas the stringer 36 and the skin 38. Adhesive may be applied to filler 30using a modified form of the apparatus 55 a shown in FIG. 17 thatincludes an adhesive dispenser. Adhesive film strips 112 may bedispensed from a pair of reels 114 and applied to the exterior sides 46(FIG. 3) of the filler 30 using a rotating cam 116. Cam 116 has avariable cross section cam face substantially matching that of thejust-formed filler 30 and functions, along with a flat lower die 94, topress the adhesive film strips 112 onto the sides 46 of the filler 30 asthe filler 30 and the film strips 112 pass between the cam 116 and theflat lower die 94.

FIG. 18 illustrates the overall steps of a method of producing thefiller 30 using the previously described apparatus 55. Beginning at step118, a stack 92 of prepreg ply strips 84 is formed, and at 120, thestack 92 of ply strips 84 is fed through one or more forming dies 70. At124, the forming die 70 is used to form the stack 92 of ply strips 84,including varying the shape of the die face 102 as the stack 92 is beingfed through the die 70.

FIG. 18A broadly illustrates the steps of an alternate method ofproducing the filler 30 using the apparatus 55. Beginning at step 125, amulti-ply layup 74 of fiber prepreg is assembled, in which the plies mayhave differing fiber orientations determined by a predetermined plyschedule. At 127, the layup 74 is slit into individual ply strip 84having varying widths which are related to the cross sectional shape ofthe particular filler 30 being fabricated. At step 129, the slit plystrips are arranged into a ordered stack 92 according to their widths,such that the stack 92 may have a cross sectional shape thatapproximates the final cross section shape of the filler 30 (see FIG.14). The ordered stack 92 of ply strips 84 is fed to one or more formingdies 70 at step 131, and at 133, the forming die(s) 70 is used to formthe stack 92 into a filler 30 having the desired cross sectional shape,which may vary along the length of the filler 30.

FIG. 19 illustrates additional steps of one practical implementation ofthe method shown in FIG. 18. At 126, the geometry of the filler 30 isdigitally defined and the materials from which the filler 30 is made areselected. At step 128, a program is developed for producing the filler30 and at 130 the program is post processed. At step 132, the program isloaded into the apparatus 55, which includes programming the controller72. At step 134, the materials from which the filler 30 is formed areprepared, which includes assembling a ply layup 74. At 136, the plylayup 74 is slit into multiple ply strips 84 of the desired widths. At138, the ply strips 84 are respectively loaded onto creels 86, and at140, the ply strips 84 are fed through the delivery head 62 of theapparatus 55. At 142, the ends of the ply strips 84 are attached to thepuller 64 and at 144 the heaters are turned on the heat the chute 96. At146, the controller 72 runs the part program to form the filler 30, andat 146 the filler 30 may be trimmed to final length, as required.Finally, at 150, the filler 30 may be frozen for future use or,alternatively, transferred directly to a composite layup assembly (notshown) for use in filling a gap.

Attention is now directed to FIGS. 20 and 21 which illustrates anotherembodiment of the apparatus 55 b. In this embodiment, an assembled,multi-ply layup 74 is fed in the direction 152 to a slitter/laminatormachine 154 that includes one or more forming dies 70 that may besimilar to that previously described. The layup 74 may include one ormore plies of unidirectional fiber prepreg of the same or differingfiber orientations, and may include one of more plies of an adhesive. Apuller 64 is used to pull the layup 74 through the machine 154. Machine154, as well as the puller 64 are operated by a suitable controller 72.

Referring now particularly to FIGS. 21 and 22, the machine 154 broadlycomprises a pair of nip rollers 156, a slitter 158, redirect rollers162, 164, compaction rollers 166 and forming die 70. An assembled(pre-plied) layup 74 is fed into the nip rollers 156 which pull thelayup 74 into the slitter 158. The slitter 158 comprises a plurality ofspaced apart cutter blades 160 which are spaced apart from each other atdiffering distances and slit the layup 74 into a plurality ofside-by-side, individual strips 84 of varying, preselected widths, eachcomprising one or more composite plies. The redirect rollers 162, 164function to turn the side-by-side strips 84 ninety degrees, redirectingthe strips 84 into alignment with each other and into a stack 92 that iscompacted by rollers 166 and fed through one or more forming dies 70(only one being illustrated in FIG. 21). The forming die 70 may besimilar to the rotatable forming die 70 previously described having aperipheral die cavity 104 (FIG. 15) that may or may or may not vary inshape and/or area around the circumference of the die 70. In otherembodiments, the die 70 may comprise one or more suitable type ofstationary extrusion dies, rather that a rotatable forming die 70 of thetype shown in FIGS. 12, 15 and 15A.

FIG. 23 illustrates the overall steps of a method of producing a fillerusing the apparatus 55 b shown in FIGS. 20-22. Beginning at step 168, amulti-ply composite layup 74 is assembled, and at 170, the layup 74 isfed substantially continuously through a slitter 158 and a forming die70. At 172, the slitter 158 is used to slit the layup 74 into aplurality of side-by-side ply strips 84. At 174, the ply strips 84 arealigned into a stack 92 as the strips 84 are being fed from the slitter158 to the die 70. At 176, the die 70 is used to form the stack 92 ofply strips 84 into a filler 30 of the desired cross sectional shape andarea.

FIG. 24 illustrates additional details of the method shown in FIG. 23.At 178, the geometry of the filler 30 is digitally defined and thematerials used to produce the filler 30 are selected. At 180 a programis generated for controlling the machine 154, and at 182 the program isloaded into the machine controller 72. At 184, a layup 74 is assembledand placed on a flat tape layer. At 186, the layup 74 is fed into theslitter 158 and at 188 the slit ply stack 92 is attached to the puller64. At 190, heaters, if used in the machine 154 to preheat the layup 74,are pre-heated. At 192, the program is run which controls operation ofthe machine 154 to produce the filler 30. At 194, the filler 30 istrimmed to length and at 196, the filler 30 may be either frozen forfuture use, or transferred directly to a composite layup assembly foruse in filling a gap.

FIG. 25 illustrates the sequential operations performed by the machine154. Beginning at 198, the assembled ply layup enters the machine 154.The nip rollers 156 pull the layup 74 into the machine 154 and at 222,the slitter 158 slits the layup 74 into multiple ply strips 84 of thedesired width. At 224, redirect rollers 162 turn the strips 84 ninetydegrees, and at 226 redirect rollers 164 bring the strips 84 togetherinto a stack 92. At 228, the compaction rollers 166 compact the stack92. At 230, a die 70, which may be stationary or movable as previouslydescribed, shapes the stack 92 into the desired filler shape. The fillerexits the machine at 232.

FIGS. 26 and 28 illustrate still another embodiment of the apparatus 55c that may be employed to produce a filler 30 a of the type shown inFIG. 27. In this example, the filler 30 a includes upper and lowerportions 236, 238 having different cross sectional shapes that vary inarea or geometry along their respective lengths. A pair of rotatabledies 70 a, 70 b are used to form the upper and lower portions 236, 238respectively of the filler 30 a. A puller, such as the puller 64 shownin FIGS. 11, 20 and 21, pulls the ply stack 92 into a nip 99 between thedies 70 a, 70 b. As best seen in FIG. 28, the upper die 70 a has a diecavity 104 having a generally triangular shape that varies in areaaround the circumference of the die 70 a. Die 70 b has a generallysemi-circular die cavity 104 a that likewise varies in cross sectionalarea around the circumference of the die 70 b. The cross sectionalshapes of the dies 70 a, 70 b shown in FIG. 28 are merely illustrativeof a wide range of cross sectional geometries that are possible,including but not limited to those as discussed earlier with referenceto the die 70 shown in FIGS. 12 and 15.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine, automotive applications and otherapplication where automated layup equipment may be used. Thus, referringnow to FIGS. 29 and 30, embodiments of the disclosure may be used in thecontext of an aircraft manufacturing and service method 240 as shown inFIG. 29 and an aircraft 242 as shown in FIG. 30. Aircraft applicationsof the disclosed embodiments may include, for example, withoutlimitation, layup of stiffener members such as, without limitationbeams, spars and stringers, to name only a few. During pre-production,exemplary method 240 may include specification and design 244 of theaircraft 242 and material procurement 246. During production, componentand subassembly manufacturing 248 and system integration 250 of theaircraft 242 takes place. Thereafter, the aircraft 242 may go throughcertification and delivery 252 in order to be placed in service 254.While in service by a customer, the aircraft 242 is scheduled forroutine maintenance and service 256, which may also includemodification, reconfiguration, refurbishment, and so on.

Each of the processes of method 240 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 30, the aircraft 242 produced by exemplary method 240may include an airframe 258 with a plurality of systems 260 and aninterior 262. Examples of high-level systems 260 include one or more ofa propulsion system 264, an electrical system 266, a hydraulic system268, and an environmental system 270. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries.

Systems and methods embodied herein may be employed during any one ormore of the stages of the production and service method 240. Forexample, components or subassemblies corresponding to production process248 may be fabricated or manufactured in a manner similar to componentsor subassemblies produced while the aircraft 242 is in service. Also,one or more apparatus embodiments, method embodiments, or a combinationthereof may be utilized during the production stages 248 and 250, forexample, by substantially expediting assembly of or reducing the cost ofan aircraft 242. Similarly, one or more of apparatus embodiments, methodembodiments, or a combination thereof may be utilized while the aircraft242 is in service, for example and without limitation, to maintenanceand service 256.

The description of the different advantageous embodiments has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageousembodiments may provide different advantages as compared to otheradvantageous embodiments. The embodiment or embodiments selected arechosen and described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method of fabricating a composite filler havinga cross section that varies along its length, comprising: forming astack of composite prepreg strips; feeding the stack through a die;using the die to form the stack into the composite filler, includingvarying a shape of a die face in contact with the stack as the stack isfed through the die; applying a strip of adhesive to the compositefiller; and compressing the adhesive against the composite filler, inwhich compressing the adhesive against the composite filler is performedby rolling a cam having a varying cross section that substantiallymatches the varying cross section of the composite filler over thecomposite filler.
 2. The method of claim 1, wherein varying the shape ofthe die face in contact with the stack comprises rotating the die as thestack is fed through the die.
 3. The method of claim 1, furthercomprising: synchronizing the feeding of the stack through the die withthe varying of the shape of the die face in contact with the stack. 4.The method of claim 1, wherein forming the stack of composite prepregstrips comprises: dispensing strips of composite prepreg respectivelyfrom a plurality of creels; and aligning the strips with each other. 5.The method of claim 4, wherein: aligning the strips with each other isperformed by passing the strips through a guide; and forming the stackof composite prepreg strips further comprises compacting the alignedstrips into a stack.
 6. The method of claim 1, further comprising:heating the stack to a forming temperature by passing the stack througha heated chute.
 7. The method of claim 1, wherein forming the stack ofcomposite prepreg strips comprises: forming a layup of prepreg plies;and slitting the layup into a plurality of strips of varying widths. 8.The method of claim 7, wherein forming the stack of composite prepregstrips further comprises: loading the plurality of strips respectivelyonto a plurality of creels; dispensing the plurality of strips from theplurality of creels; and aligning the dispensed strips.
 9. The method ofclaim 1, wherein forming the stack of composite prepreg strips includesordering strips of composite prepreg as the strips are being dispensedand aligned.
 10. The method of claim 1, wherein feeding the stackthrough the die comprises pulling one end of the stack.
 11. The methodof claim 1, wherein forming the stack of composite prepreg stripscomprises: assembling a layup of prepreg plies; and slitting the layupinto a plurality of side-by-side strips of varying widths by moving thelayup through a slitter.
 12. The method of claim 11, wherein forming thestack of composite prepreg strips comprises: redirecting theside-by-side strips into alignment with each other; and compacting thealigned strips into the stack.
 13. The method of claim 12, whereinredirecting and compacting the strips are each performed by passing thestrips through a set of rollers.
 14. The method of claim 11, whereinassembling the layup includes: laying up unidirectional fiber prepregplies, including varying the fiber orientations of the plies of thelayup.